11C-Methionine (11 C-METH) is an aminoacidic PET tracer whose main employment regards the diagnosis of central nervous system tumors. Methionine is, in fact, one of the five essential amino acids that can be involved in different metabolic pathways at a cellular level. The main destiny of this molecule is the proteic synthesis within ribosomes, but it can also be converted to enter the citric-acid cycle (to produce energy) and as a cofactor for transferring monocarbon units.